1. Field of the Invention
The invention relates to a method and a device for operating a combined burner for liquid and gaseous fuels for the purpose of generating hot gases.
2. Discussion of Background
To achieve the lowest possible NOx emissions, burners are operated close to their lean extinguishing limit. This results in the disadvantage that the regulating range of the burners is greatly restricted. In order to remove this disadvantage, individual burners are switched off during partial load of the gas turbine so that the remaining burners can be operated in their stability range. But this is accompanied by an impairment in the temperature distribution over the periphery.
A further possibility of improving the regulating range of the burner is to enrich the fuel gases with additional fuel near the axis of the burner, which is also called internal piloting. As a result, the stability range of the burners is extended by the injection of a pilot gas to such an extent that reliable operation is guaranteed. To alternatively operate a burner with gas or fuel oil, a method is known in which the fuel oil used as an alternative to the pilot gas is atomized by means of an airblast nozzle. In this method, air is injected to atomize the fuel oil near the axis, i.e. in the center of the burner. But this is done not only during the fuel-oil atomization but also during pilot operation with gas, in which, however, no blast air is required for the atomization. This additional air destabilizes the pilot-gas flame on the one hand by making the mixture leaner and on the other hand by the oncoming air flow itself. The destabilizing leads to a clear reduction in the lean extinguishing limit of the gas flame.